Whatever the reason your son did this, that's your business, but as a teacher of children with emotional impairments, I'd turn this into a learning opportunity. I'd take the best suggestions from the knowledgeable TBers on this site and have your son work with you to do the repairs. He will come to appreciate the value of this equipment and that it is a means to your personal enjoyment. Who knows, maybe he will get an interest in learning the skills to repairing amps that he can channel his energy into a very successful career..........
If this was done intentionally, I'll leave the discipline (not punishment) up to you.
Exactly how I would handle this. It could quite possibly turn in to a magic moment for the both of you as teaching/learning moment. Gawd I love kids. Should have had a million of them.

